Flare installation for the combustion of hydrocarbon gas with prior admixing of air

ABSTRACT

An improved flare installation to burn excess hydrocarbon gas, comprising a mixing chamber receiving atmospheric air and having an inlet for gases from a low-pressure separator, and an injector for gas from a high-pressure separator, on the same axis as a mixer, while a burner is provided below this chamber. The improved device is specially suitable for the non-polluting burning of gases accompanying liquid hydrocarbons in production fields, during testing, or in refinery plants.

United States Patent Lazarre et al.

[ Sept. 3, 1974 [75] Inventors: Flavien Lazarre; Jacques Rozand;

Gilbert Blu; Jean-Pierre Bimond, all of Pan, France [73] Assignee:Societe Nationale Des Petroles DAquitaine, Paris, France [22] Filed:Aug. 3, 1973 [21] Appl. No.: 385,329

[30] Foreign Application Priority Data Aug. 4, 1972 France 72.28207high-pressure separator, on the same axis as a mixer, [52] US. Cl.431/202, 23/277 C while a burner s p d d l w this chamber. The 51 Int.Cl. F23d 13/20 improved device is specially suitable for the [58] Fieldof Search 431/202, 5; 23/277 c polluting burning of gases accompanyingliquid y carbons in production fields, during testing, or in re-References Cited finery plants.

UNITED STATES PATENTS 2,761.496 9/1956 Verner et al 43l/202 .3 Claims, 1Drawing Figure 3% 18 I 2 HI Campbell et al 43l/202 X Sparrow et al431/202 Primary Examiner-Edward G. Favors Attorney, Agent, orFirm-Brisebois & Kruger 5 7 ABSTRACT An improved flare installation toburn excess hydrocarbon gas, comprising a mixing chamber receivingatmospheric air and having an-inlet for gases from a low-pressureseparator, and an injector for gas from a FLARE INSTALLATION FOR THECOMBUSTION OF HYDROCARBON GAS WITH PRIOR ADMIXING OF AIR This inventionconcerns an improved device for the combustion of hydrocarbon gases,with prior admixing of air.

More particularly, it concerns an improved device providing fornon-polluting combustion of gases, especially gases accompanying liquidhydrocarbons, which must be disposed of for want of commercial outlets.

The problem of eliminating such gases occurs in the testing of new gasor oil wells, in the operation of oil fields, and in the operation ofprocessing and refining plants.

In oil fields, current practice is to use a flare to burn the gases fromthe separators that cannot be marketed for numerous reasons, mainlyinvolving geographical location, size of local stocks, and possibleoutput.

Gas discharged by high-pressure and low-pressure separators are usuallysent to different flares. Combustion is always incomplete, since theoxygen supply is insufficient, obtained as it is by diffusion around theflame. This results in constant black smoke and the fallout of unburntmatter in the form of carbon particles or droplets of hydrocarbonscondensed by the process of expansion, while the flame itself is of highradiance and brilliance.

Moreover, when the gas source is under high pressure, such as severaltens of bars, the cooling effect associated with expansion is soconsiderable that the production of hydrates may cause obstruction ofthe flare line.

The polluting effect of such devices is certain, and moreover it isgenerally very conspicuous, with psychological consequences that may beeven more serious than the actual pollution.

The device according to the invention obviates these drawbacks byfeeding the flares with a mixture of gas and air in proportions ensuringcomplete combustion, thus avoiding pollution, practically eliminatingheat radiation, and precluding the formation of hydrates.

This new installation for the combustion of excess gas from wells orhydrocarbon processing plants, with means for the separation of oil orcondensate from gas, and passages to convey such gas after it has beenseparated from the oil or condensate, is characterized by the fact thatit is supported on a raised structure above ground level and comprises afeed chamber provided with adjustable air inlets, a mixing chamberadjacent to the divergent passage which may be preceded by a convergentpassage, at least one injector of combustible gas under pressure,located at the opening between the feed chamber and mixing chamber, anda burner at the opposite end of this mixing chamber, opening into theatmosphere, and comprising means for igniting the flare, and means ofcontrolling combustion.

In one recommended embodiment, the installation comprises an inletpassage for combustible gas, leading from the storage tanks andlow-pressure separators to the feed chamber, above the pressurizedcombustible gas injector.

In the same embodiment, the means of adjusting the air supply consist ofa system to control the position of the pressurized combustible gasinjectors in relation to the opening between the feed chamber and mixingchamber.

In another embodiment, applicable to high flow rates, the meanssupporting the device consist of a tower made up of assembled sectionalor tubular components with struts and wind-braces, provided withconvenient means for fixing the high-pressure and lowpressure gas feedpipes and electric cables for igniting the flare and controllingcombustion.

In still another embodiment, applicable to comparatively small flowrates, the means supporting the burner consist of a braced upright tube,provided with side openings for the admission of air, the mixing chamberbeing located above these openings, and the tube being equipped withconvenient means for fixing the highpressure and low-pressure gas feedpipes and electric cables required for igniting the flare andcontrolling combustion.

Such a device is illustrated by way of example below.

The FIGURE shows, at a production centre, means of separating oil orcondensate from gas, consisting of a high-pressure separator (1) fedfrom a well or a collector (not shown here), with a high-pressure gasoutlet (2) and an outlet (3) for partially degassed liquid. This liquidis fed into a low-pressure separator (4) with lowpressure gas outlet (5)and an oil or condensate outlet (6).

The flare installation is fixed above ground level on a support (7),which may be a structure consisting of assembled sectional elements withstruts and windbraces, bolted together and provided with the necessarymeans of fixing the high-pressure and low-pressure gas feed pipes (8 and9 respectively) and electric cables required for igniting the flare andcontrolling combustion (not shown here).

The feed chamber (10) is provided with adjustable air inlets (such as 11and an inlet for the admission of combustible gas from the low-pressureseparator, located above an injector (13) of combustible'gas from thehigh-pressure separator. This injector is located on the axis of amixing chamber (14) adjacent to the feed chamber, which also includes aconvergent passage (15) followed by a divergent passage (16). Theposition of the outlet of the injector (13), relative to the plane ofthe mixing chamber entrance, is adjustable by translational movementalong the mixing chamber axis by means of a telescopic system (19), forexample. The choice of the position of the injector outlet constitutesone of the parameters determining the air/gas ratio in the mixingchamber. At the end of the divergent passage (16) a combustion flue (17)opens into the atmosphere through an interposed grid or funnel (18), toprevent flashback. The devices (20) for igniting the torch andcontrolling the flame are conventional.

This flare device makes it possible to obtain a gaseous mixture ensuringcomplete combustion. The flame obtained is thus transparent and of lowradiance, the combustion gases released are neutral and nonpolluting,and the combustion process does not produce any unburnt matter, liquidor solid. Moreover, the

dilution, in air let in at the surrounding temperature, of

the combustible gases cooled by expansion precludes any extensivecooling, likely to produce hydrates.

The operation of the combustion device requires no power supply: the airrequired for combustion is supplied by atmospheric induction through aninjector which works by using part of the power supplied by thehigh-pressure gas. Where the plant is fed with gaseous residues fromrefineries, it may be advisable to supply either additional combustiblegas at high pressure, or sufficient power to draw in thevolume of airrequired for the combustion of gases composed of heavy substances andsupplied at comparatively low pressure.

What is claimed is: i

1. A flare device for the combustion of excess combustible gas, saiddevice comprising means for separating said combustible gas from oil andcondensate contained therein and for supplying separated combustible gasthrough two different ducts at two different pressures,

a feed chamber provided with adjustable air inlet means,

a high pressure injector connected to introduce combustible gas from theduct carrying gas at the higher of said pressures into said feed chamberand thereby suck air into said feed chamber through said air inletmeans,

' means for adjusting the position of the outlet end of said injectorrelative to the connection between said feed and mixing chambers.

3. A flare device as claimed in claim 1 in which said divergent passageis preceded by a convergent passage in said mixing chamber communicatingdirectly with said feed chamber.

1. A flare device for the coMbustion of excess combustible gas, saiddevice comprising means for separating said combustible gas from oil andcondensate contained therein and for supplying separated combustible gasthrough two different ducts at two different pressures, a feed chamberprovided with adjustable air inlet means, a high pressure injectorconnected to introduce combustible gas from the duct carrying gas at thehigher of said pressures into said feed chamber and thereby suck airinto said feed chamber through said air inlet means, means forintroducing combustible gas from the other of said ducts into said feedchamber at a point near the upper end of said injector, a mixing chamberconnected to receive combustible gas and air from said feed chamber anddefining a gas flow passage which diverges as it approaches the endthereof remote from said feed chamber, and a burner supplied throughsaid diverging passage, said burner being equipped with means forigniting said combustible gas.
 2. A flare device as claimed in claim 1comprising means for adjusting the position of the outlet end of saidinjector relative to the connection between said feed and mixingchambers.
 3. A flare device as claimed in claim 1 in which saiddivergent passage is preceded by a convergent passage in said mixingchamber communicating directly with said feed chamber.